Catalysts containing magnesium for polymerization or co-polymerization of ethylene are known to have very high catalytic activities and to accord polymers of high bulk density, which are suitable for liquid phase or gas phase polymerization. By liquid phase polymerization of ethylene, it denotes a polymerization process performed in a medium such as bulk ethylene, isopentane, or hexane, and as for the important characteristics of catalysts used therein, in consideration of the applicability to the process, there are as follows: high catalytic activity, bulk density of the resultant polymers, and the content of low molecular weight molecules of the resultant polymers soluble in a medium. Among these, the catalytic activity is to be the most important characteristic of a catalyst.
Many of the titanium-based catalysts containing magnesium for olefin polymerization, and the manufacturing methods thereof have been reported. Especially, many processes making use of magnesium solutions to obtain catalysts which can generate olefin polymers of high bulk apparent density have been known. There is a means of obtaining a magnesium solution by reacting magnesium compounds with such electron donors as alcohol, amine, cyclic ether, or organic carboxylic acid in the presence of a hydrocarbon solvent. As for the cases of use of alcohol, they are disclosed in U.S. Pat. Nos. 4,330,649, and 5,106,807. Further, the methods for production of catalysts containing magnesium by reacting said liquid-phase magnesium solution with a halogenated compound such as titanium tetrachloride are well known. Such catalysts provide high bulk density to the resultant polymers, but there is much yet to be improved with respect to their catalytic activities, and there are production disadvantages, such as its production of a large amount of hydrogen chloride during the production of catalysts.
U.S. Pat. No. 5,459,116 reported a method of production of a titanium solid catalyst by contact-reacting a magnesium solution containing an ester having at least one hydroxy group as an electron donor with a titanium compound. By this method, it is possible to obtain a catalyst of high polymerization activity, which accords high bulk density to resultant polymers, but there is room for yet more improvements.
U.S. Pat. No. 4,843,049 reported a method for producing a catalyst of high titanium content by reacting titanium alkoxide with a magnesium chloride-ethanol carrier produced by means of a spray-drying method, and then reacting thereto diethylaluminium chloride or ethylaluminium sequischloride. However, there are disadvantages in that the method results in alcohol content which is outside the range of 18˜25%, or deterioration of bulk density of polymers thus produced when compounds other than diethylaluminium chloride or ethylaluminium sesquichloride are used.
U.S. Pat. Nos. 5,726,261 and 5,585,317 disclose a method for producing a catalyst having porosity of 0.35˜0.7 by heat treating a magnesium chloride-ethanol carrier produced by means of a spray-drying method, or by heat treating the same, followed by treatment with triethylaluminium, and then treating thereto a titanium alkoxide, or titanium alkoxide along with silicone tetraethoxide, etc., by which a titanium-based compound having at least one titanium-halogen and at least one alkoxy group is then supported.
As shown above, there is a need for the development of new catalysts for homo-polymerization or co-polymerization of ethylene for producing polymers with the following characteristics: a simple manufacturing process, high polymerization activity, and high bulk density for polymers by means of controlling the catalyst particles. In the present invention, therefore, it is intended to provide a method for producing, from low-cost compounds via a simple process, a catalyst having excellent catalytic activity, capable of producing polymers of high bulk density for polymers by means of controlling the morphology of catalyst particles. Further, the specific production process of catalysts and the steps thereof as disclosed in the present invention have never been reported in the prior art.